1. Field of the Invention
The present invention relates to the field of power management. More particularly, the present invention relates to a circuit and a method for configuring an electronic device to operate in one of a plurality of power states based on the operating environment of its hardware product.
2. Description of Art Related to the Invention
Over the last few years, there have been many advances in semiconductor technology. These advances have lead to the development of high-speed electronic devices operating at higher frequencies and supporting additional and/or enhanced features. As a result, high-speed electronic devices normally require more power and dissipate more heat as a by-product than antiquated electronic devices operating at lower frequencies.
In order to satisfy customer requirements, battery-powered portable computers (e.g., laptop or notebook style computers, hand-held computers, etc.) are implemented with high-speed processors similar to those implemented in desktop computers. Normally, the heat produced by internal logic of conventional portable computers is dissipated through passive cooling. For portable computers, "passive cooling" involves spreading the heat uniformly along an interior of its casing. Thereafter, the casing of the portable computer is simply cooled through conduction, convection and radiation.
In light of the semiconductor technology advances, standard passive cooling techniques are now becoming unable to provide sufficient thermal dissipation for portable computers. When the high-speed processor is operating at full frequency, the surface temperature of the casing of the portable computer tends to rise above a temperature considered acceptable by the Occupational Safety and Health Association (OSHA) and/or portable computer users. As a result, power usage by conventional portable computers must be reduced in order to prevent the surface temperature of the casing from rising above this temperature.
Commonly, power usage of portable computers is reduced by decreasing processor core operating frequency at manufacturing to a static value which will not exceed the portable computer's passive cooling capability. In general, processor core operating frequency is an external clock, or bus frequency, multiplied by a fixed bus ratio which is set by hardware at processor reset. The processor core operating frequency may be decreased by lowering the bus ratio or by lowering the frequency of the external clock supplied to the processor (hereinafter referred to as "frequency reduction"). Frequency reduction at a fixed bus ratio may be accomplished by dividing the clock signal before it is supplied to the processor. Alternatively, frequency reduction at a fixed bus ratio may be emulated by periodically halting the clock signal for brief time intervals so that the average operating frequency is reduced.
Referring to FIG. 1, a graph illustrating power savings realized by conventional frequency reduction of an electronic device (e.g., a processor) is shown. It is well-known that a processor is designed to operate across a frequency range at a specific voltage. This operating range 100 is represented as being between points A and B, where (i) point A represents the minimum operating frequency at which the processor will operate, and (ii) point B represents the maximum operating frequency that the processor can support. In theory, to a first order approximation, power is directly proportional to frequency as presented herein. Thus, as shown through points C and D, a reduction in the operating frequency of the processor by ten percent (10%) will reduce its total power consumption by ten percent (10%) from P1 to P2. Of course, true system power savings are not exactly proportional to frequency reduction because most every hardware product, including a portable computer, is implemented with processor frequency-independent components which consume power (e.g., a display).
However, the use of static power saving techniques has generated performance gaps between desktop computers and portable computers. This performance gap is a continuing concern to original equipment manufacturers (OEMs). One reason is that substantial differences in performance will adversely effect the demand for portable computers and for components used therein. To date, it appears that no efforts have been made in controlling the reduction or augmentation of the operating frequency and/or supply voltage utilized by an electronic device, including a processor, based on the operating environment experienced by its hardware product.
Besides complying with its thermal dissipation constraints, a battery-powered portable computer is configured to reduce its power usage in order to extend the life of its removable battery packs. The typical technique in reducing power usage is not dependent on the operating environments of the portable computer. Rather, it is usually dependent on a system dependent, power management system which, through a combination of software and hardware, is able to put unused sub-systems into sleep or shut-down modes thus saving power.